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grabbed a few pics on the way home from a job tonight ...

they look pretty noisey to me, what iso where you using

I like the story bridge shot (image 3) but i would have preferred it if you had kept it as the main subject and got more of it in. The starburst effect looks great with the myriad of lights on the bridge. (UV filter perhaps?)

However, hopefully you shot in NEF as the white balance could do with an adjstment to get the orange tinge down to a more appealing and lifelike level.

Nice work.

The last one is a standout for me. I did not notice any noise.

Last one also is a winner seems to be very sharp compared to the others

all pics were taken with the Pentax 12-24 at iso 200 using tripod.
The orange caste comes from the Storey Bridge lights .
pic 1: 3 secs f4
pic 2: 20 secs f16
pic 3: 30secs f16
pic 4: 10 secs f8

the pics are a fair bit sharper at full size but they still compare against each other the same as these smaller size shots.
To me it appears that the time is not a factor but the aperture is the deciding factor in the sharpness of the lights.

f8 looks like the sweeter spot for this lens ... what do you guys reckon?

From the exif you provided it is a pity that the exposure time was not the same, then you could have made a real comparison on the best apeture.

here is a few unprocessed pics ... colours are a fair bit duller compared to real life ...
Pentax DS with Pentax DA 12-24 f4 at iso 200 on tripod.

pic A: 1.5 secs f4


pic B: 20 secs f16


pic C: 10 secs f8


it would have been better having the same image for all three with different apertures but i wasn't testing at the time.